Need advice

My 7 day old is SUPER GASSY! I mean, whoa. His stools are a little runny. He's breastfed so it's hard to tell. I have to take a pretty strong antibiotic and it says that it may interrupt his gastrointestinal flora. Should I be feeding him formula? Are 7 day Olds usually super super gassy!? Any advice would be great. And of course it's happening on a Saturday when his doc is closed:-(